Catalytic agents which have been used to catalyze the ring opening polymerization of various heterocyclic compounds, particularly epoxides, include acids, bases, and certain metal complexes such as, for example, organoboron compounds, FeCl.sub.2, ZnEt.sub.2 /H.sub.2 O, AlEt.sub.3 /H.sub.2 O, and aluminoporphrins. Reference is made, for example, to Ivin and Saegusa, Ring Opening Polymerization, Vol. 1, Elsevier App. Sci. Pub. New York 1984, p. 185; and to May and Tanaka, Epoxy Resins Chemistry and Technology, Marcel Dekker, Inc., New York, 1973, p. 283.
Epoxy functional siloxanes may be polymerized by ring opening of the oxirane rings by either UV radiation or heat. Polymerization by UV radiation involves the use of a photocatalyst that, when irradiated with UV light, forms an acid that catalyzes the epoxide. Such reactions are taught by Eckberg in U.S. Pat. No. 4,279,717 and Crivello in U.S. Pat. No. 4,617,238.
Polymerization by heat involves the simple step of heating the epoxy functional siloxanes to a temperature of 120.degree. C. or greater, causing the oxirane rings to open and react. Specific reference is made to E. P. Plueddemann and G. Fanger, Epoxyorganosiloxanes, Journal of the American Chemical Society, vol. 81, pp. 2632-2635, 1959.
Platinum-containing catalysts are highly useful catalysts in hydrosilyation reactions, i.e., the addition of Si-H containing compounds to olefin and acetylenic bonds. Reference is made to Aylett, Organometallic Compounds, Vol. 1, John Wiley, New York, 1979, p. 107 and to Speir, Adv. in Org. Chem., Vol. 17, p. 407, 1974. It is further known in the art that platinum will catalyze the hydrosilylation reaction between ethylenically unsaturated organic epoxy monomers and Si-H containing compounds. Such reactions are described, for example, in copending, commonly assigned application Ser. No. 332,646, filed Apr. 3, 1989.
The use of platinum catalysts to promote ring opening of heterocyclic polymers provides numerous advantages over catalysts presently used to catalyze polymerizations. These advantages include the use of low levels of catalyst and the low tendency of catalyst residues to induce color, oxidative instability in the final cured resin, or corrosion to metals in contact with the resin. Furthermore, with silicones, the platinum catalysts are less prone to cause reversion of the silicone polymers to cyclic siloxanes.